The availability of clean water for uses in human civilization is shrinking with the increase in population and expansion in urbanization and industrialization. As estimated by the UN nearly one-fifth of the World populations live in areas of physical water scarcity. Though the two-third of the earth is water, only around 2.5 percent is fresh water. Therefore to meet the increasing demand of fresh water, sea and brackish water desalination by membrane has been recognized as the promising technology because of the technological cleanliness involved in the process and less energy intensive nature. Reverse osmosis membranes are now worldwide accepted as having the potential to meet this huge challenge. Membrane performance is the key to the successful operation of reverse osmosis plant. High flux and high salt rejection membranes are desirable for cost effective operation of the system. Fully aromatic polyamide thin film composite reverse osmosis membranes that are capable of delivering high flux and salt rejection are available in the market from different manufacturers but, they are only few in numbers. There are also several reports published in journals and patents on TFC membranes preparation and performance.
References may be made to U.S. Pat. No. 3,926,798, wherein a process for making composite reverse osmosis membrane by coating a microporous polysulfone membrane with an aqueous solution of furfuryl alcohol and an acid catalyst capable of polymerizing the furfuryl alcohol by heat treatment is claimed by John E. Cadotte in the year 1974.
References may be made to U.S. Pat. No. 4,277,344, wherein a process for making cross-linked, interfacial polymerized reverse osmosis membranes of aromatic polyamides, particularly poly(phenylenediamine-trimesamide) for good salt rejection and flux characteristics are disclosed by John E. Cadotte in the year 1979.
References may be made to U.S. Pat. No. 7,815,987B2, wherein reported a method for coating of composite membrane with polyalkyleneoxide and polyacrylamide compounds for improvements in fouling resistance.
References may be made to U.S. Pat. No. 6,171,497, wherein preparation of high flux reverses osmosis membranes by treating polyamide membranes with chlorine as oxidizing agent was disclosed. The salt rejection is ≥99% and water flux 1.5 m3/m2-day or higher when evaluated using 500 ppm sodium chloride solution at pH 6.5, temperature 25° C., pressure 7.5 kgfcm-2.
References may be made to U.S. Pat. No. 4,894,165, wherein coating by vinyl-addition polymer is reported to enhance the salt rejection of polyamide reverse osmosis membranes.
References may even be made to U.S. Pat. No. 4,454,176, wherein a process for preparing reverse osmosis membrane has been revealed by coating aromatic polyamide, solvent and salt onto woven, unsized, polyester or aromatic polyamide fabric as porous support.
References may be made to US2009/0050558A1, wherein a process for producing reverse osmosis membrane has been revealed. The patent claims coating process for continuous preparation of reverse osmosis membranes.
References may be made to U.S. Pat. No. 8,029,857, wherein a process for producing micro- and nano-composite support structure (porous membrane) for reverse osmosis membrane has been described. Nano particles are added to the support membrane during casting. The resultant reverse osmosis membrane obtained after coating the micro-nano composite support membrane produced a membrane with more resistant to compaction when compared to the one having no such particle.
References may be made to U.S. Pat. No. 7,658,872, wherein a process for improving permeability of already prepared reverse osmosis membrane by treating with organo-ammonium nitrates salts is disclosed.
References may be made to IN244150, wherein the method for the preparation of composite membrane using different types of amines and acid chlorides has been described.
References may be made to ‘Journal of Membrane Science 2010, 348(1-2), 268-276’ wherein Liu, M et al. reported ‘Impact of manufacture technique on seawater desalination performance of thin-film composite polyamide-urethane reverse osmosis membranes and their spiral wound elements’.
References may be made to ‘Journal of Membrane Science 2008, 311(1-2), 34-45, wherein Ghosh, A. K. et al. reported the effect of interfacial reaction conditions on reverse osmosis membrane properties.
References may be made to ‘Journal of Membrane Science 2008, 311(1-2), 34-45, wherein Ghosh, A. K. and Hoek E. M. V. reported effect of support membrane structure and chemistry on composite membrane properties.
The prior art have many drawbacks as follows. None of the patents given above in the prior art, covers the complete process for manufacturing thin film composite membrane, which involves three stages namely: i) preparation of polysulphone porous support membrane, ii) preparation of ultrathin polyamide active layer on the top of polysulphone porous support and finally, iii) surface modification with suitable hydrophilic polymers. Moreover, the results which were reported were based on the experiments that were carried out at a very small tray scale levels in batch-wise manner, where it was possible to vary a single parameter at a time while keeping the other variables constant. However, the continuous process of the large scale preparation of composite membrane involves the variation of more than one parameter at a time. For example, in the preparation of polysulphone porous support, when the casting rate is varied, there is a possibility for the variation in polymer solution take up time on the fabric, air travel gap before entering in to the gelation bath, shear stress, etc. These variables in turn will have considerable effect on polysulphone porous support properties like pore size and porosity with the concomitant effect on TFC membrane performance. Similarly, in the preparation of polyamide active layer on the porous support, tandem variations in the contact time with monomer solutions, reaction time between the monomers, curing time of the nascent polyamide active layer have to be optimized to produce the membrane with the desired separation performance. Hence, the major requirement is a single patent wherein the process covers all the aspects of composite membrane preparation on a commercial production.
Patents application no. 1027DEL2012 describes the preparation of TFC membranes with inherent antimicrobial properties. The TFC membranes were prepared by reaction between MPD or mixture of MPD+melamine and pyridinetricarboxylic acid chloride or mixture of pyridinetricarboxylic acid chloride+TMC. The prepared membranes exhibited superior antibiofouling property compared to conventional TFC membranes prepared with reacting TMC and MPD. Thus the main object of the said patent application was to prepare membranes with inherent antimicrobial activity. The organic fouling resistant capability and chlorine resistant property of the membranes was not described in the said patent application.
The intended patent application reveals the complete process for making thin film composite reverse osmosis membrane in a continuous manner at commercial scale production levels using semi-automated machinery. The patent covers: i) the process for continuous preparation of polysulphone porous support having the required properties, ii) the process for continuous preparation of polyamide active layer on the top of polysulphone porous support, iii) the process for surface modification of the thin film composite membrane for improving fouling resistance.